In IMT2000-TDD, a midamble, which is a pilot sequence, is inserted in the center of a time slot. Multiplexed signals from multiple users arrive at the receiving end, and the receiving end performs correlation operation using midambles different for each signal, thereby creating delay profiles on a per midamble basis, detecting paths and subjecting these to rake-demodulation or JD-demodulation, and acquiring the received data.
To acquire the received data on a per user basis, it is necessary to detect the timing of each user's top path in delay profiles. Now, there is processing referred to as frame tracking for tracking the frame timings. By virtue of this frame tracking processing, the top path in a delay profile is detected on a per user basis, and the received data is demodulated by adjusting the timing in accordance with the top path. Usually, tracking processing is performed using a common channel that all users share. On this common channel, a signal is multiplexed with a user signal. At the receiving end, following user-specific delay profiles, delay profiles of the common channel are created.
Now, when the receiving party moves while engaged in communication, and when, for instance, the receiving party moves out from behind a building while communicating, the receiving party is then able to receive direct waves from the base station apparatus after moving out from behind the building. Consequently, new peaks by the direct waves might appear before the peaks by the delay waves. If these peaks by the direct waves can be selected as paths and used for rake combining, the quality of the received signal after the rake combining can be improved. So, when paths such as above are detected, tracking processing is performed such that the top path is changed to a path by a direct wave.
On the other hand, a mobile apparatus receives multiplexed transmission data from multiple users. Consequently, when there is a new path before the top path, there is a possibility that the correlation operation result at a timing before the top path shows the component of another user signal using a midamble corresponding to a circulation amount as of just before.
That is, the communication schemes of IMT2000-TDD use midambles that are created on a per channel basis by cyclically shifting the basic midamble. Consequently, the correlation operation result at a timing before the top path and the correlation operation result of a channel using a midamble shift corresponding to a circulation amount as of just before may show the same component.
However, with a typical receiving apparatus, when there is a new path before the top path in a delay profile, by tracking processing, this new path is always set as the new top path. Consequently, when the new path happens to be another user's delayed wave or the like, the reception is done at wrong timings and this may disable communications.